diff --git a/core/blockchain.go b/core/blockchain.go
index 1079834c56..4c0f3078bc 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -1093,16 +1093,10 @@ func (bc *BlockChain) InsertChain(chain types.Blocks) (int, error) {
 	}
 	// Remove already known canon-blocks
 	var (
-		start       = 0
 		block, prev *types.Block
 	)
-	for start, block = range chain {
-		if !bc.IsCanon(block.Hash(), block.NumberU64()) {
-			break
-		}
-	}
 	// Do a sanity check that the provided chain is actually ordered and linked
-	for i := start + 1; i < len(chain); i++ {
+	for i := 1; i < len(chain); i++ {
 		block = chain[i]
 		prev = chain[i-1]
 		if block.NumberU64() != prev.NumberU64()+1 || block.ParentHash() != prev.Hash() {
@@ -1117,7 +1111,7 @@ func (bc *BlockChain) InsertChain(chain types.Blocks) (int, error) {
 	// Pre-checks passed, start the full block imports
 	bc.wg.Add(1)
 	bc.chainmu.Lock()
-	n, events, logs, err := bc.insertChain(chain[start:], true)
+	n, events, logs, err := bc.insertChain(chain, true)
 	bc.chainmu.Unlock()
 	bc.wg.Done()
 
@@ -1165,6 +1159,22 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 	it := newInsertIterator(chain, results, bc.Validator())
 
 	block, err := it.next()
+
+	// Left-trim all the known blocks
+	if err == ErrKnownBlock {
+		// First block (and state) is known
+		//   1. We did a roll-back, and should now do a re-import
+		//   2. The block is stored as a sidechain, and is lying about it's stateroot, and passes a stateroot
+		// 	    from the canonical chain, which has not been verified.
+		// Skip all known blocks that are behind us
+		current := bc.CurrentBlock().NumberU64()
+		for block != nil && err == ErrKnownBlock && current >= block.NumberU64() {
+			stats.ignored++
+			block, err = it.next()
+		}
+		// Falls through to the block import
+	}
+
 	switch {
 	// First block is pruned, insert as sidechain and reorg only if TD grows enough
 	case err == consensus.ErrPrunedAncestor:
@@ -1184,20 +1194,6 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 		// If there are any still remaining, mark as ignored
 		return it.index, events, coalescedLogs, err
 
-	// First block (and state) is known
-	//   1. We did a roll-back, and should now do a re-import
-	//   2. The block is stored as a sidechain, and is lying about it's stateroot, and passes a stateroot
-	// 	    from the canonical chain, which has not been verified.
-	case err == ErrKnownBlock:
-		// Skip all known blocks that behind us
-		current := bc.CurrentBlock().NumberU64()
-
-		for block != nil && err == ErrKnownBlock && current >= block.NumberU64() {
-			stats.ignored++
-			block, err = it.next()
-		}
-		// Falls through to the block import
-
 	// Some other error occurred, abort
 	case err != nil:
 		stats.ignored += len(it.chain)
@@ -1323,6 +1319,10 @@ func (bc *BlockChain) insertSidechain(block *types.Block, it *insertIterator) (i
 	for ; block != nil && (err == consensus.ErrPrunedAncestor); block, err = it.next() {
 		// Check the canonical state root for that number
 		if number := block.NumberU64(); current.NumberU64() >= number {
+			if canonical := bc.GetBlockByNumber(number); canonical != nil && canonical.Hash() == block.Hash() {
+				// Not a sidechain block, this is a re-import of a canon block which has it's state pruned
+				continue
+			}
 			if canonical := bc.GetBlockByNumber(number); canonical != nil && canonical.Root() == block.Root() {
 				// This is most likely a shadow-state attack. When a fork is imported into the
 				// database, and it eventually reaches a block height which is not pruned, we
diff --git a/core/blockchain_test.go b/core/blockchain_test.go
index 6e364ef2bd..ff821f3242 100644
--- a/core/blockchain_test.go
+++ b/core/blockchain_test.go
@@ -1580,14 +1580,15 @@ func testSideImport(t *testing.T, numCanonBlocksInSidechain, blocksBetweenCommon
 	// canon(pruned), side, side...
 
 	// Generate fork chain, make it longer than canon
-	parent := blocks[lastPrunedIndex+blocksBetweenCommonAncestorAndPruneblock]
+	parentIndex := lastPrunedIndex + blocksBetweenCommonAncestorAndPruneblock
+	parent := blocks[parentIndex]
 	fork, _ := GenerateChain(params.TestChainConfig, parent, engine, db, 2*triesInMemory, func(i int, b *BlockGen) {
 		b.SetCoinbase(common.Address{2})
 	})
 	// Prepend the parent(s)
 	var sidechain []*types.Block
 	for i := numCanonBlocksInSidechain; i > 0; i-- {
-		sidechain = append(sidechain, blocks[len(blocks)-i])
+		sidechain = append(sidechain, blocks[parentIndex+1-i])
 	}
 	sidechain = append(sidechain, fork...)
 	_, err = chain.InsertChain(sidechain)
@@ -1610,6 +1611,9 @@ func testSideImport(t *testing.T, numCanonBlocksInSidechain, blocksBetweenCommon
 // [ Cn, Cn+1, Cc, Sn+3 ... Sm]
 //   ^    ^    ^  pruned
 func TestPrunedImportSide(t *testing.T) {
+	//glogger := log.NewGlogHandler(log.StreamHandler(os.Stdout, log.TerminalFormat(false)))
+	//glogger.Verbosity(3)
+	//log.Root().SetHandler(log.Handler(glogger))
 	testSideImport(t, 3, 3)
 	testSideImport(t, 3, -3)
 	testSideImport(t, 10, 0)